1. Field of the Invention
The present invention relates to a vehicle environment recognition apparatus and a preceding-vehicle follow-up control system, and more particularly, to a vehicle environment recognition apparatus that recognizes a surrounding environment by stereo matching of a pair of images taken by a stereo-image taking means, and a preceding-vehicle follow-up control system including the vehicle environment recognition apparatus.
2. Description of the Related Art
In recent years, adaptive cruise control (hereinafter abbreviated as ACC) systems having a preceding-vehicle follow-up function have been developed. An ACC system recognizes an environment in front of and around a subject vehicle (a vehicle in which the system is mounted) and a preceding vehicle by processing a pair of images taken by a stereo-image taking means formed by a stereo camera, and performs follow-up running control with respect to the preceding vehicle on the basis of the recognition result.
When there is no preceding vehicle, the ACC system causes the subject vehicle to run at a set constant speed. In contrast, when there is a preceding vehicle, the ACC system automatically and properly controls an accelerator throttle and a brake mechanism of the subject vehicle so that the subject vehicle follows the preceding vehicle. To this end, the ACC system is required to accurately detect the preceding vehicle.
For example, when an image is taken by a CCD (charge coupled device) image sensor serving as the stereo-image taking means in a backlit environment, a linear smear that is extremely brighter than the surroundings (also referred to as an overexposed portion) sometimes appears in the image in a manner such as to extend vertically. FIG. 15 shows an example of an image taken at a high attitude. In the image, a portion corresponding to the sun Su setting near the top of a small mountain M is extremely bright (even the outline of the sun Su is not shown because of intense flare (halation)). This causes a significantly large smear Sm below the sun Su in the image.
In this condition, stereo matching cannot be properly conducted on a pair of images taken by the stereo-image taking means, and a preceding vehicle Vah cannot be detected (that is, is lost), or a wrong distance that is different from the actual distance is detected by stereo matching. If the ACC system continues operation in a state in which the preceding vehicle Vah is lost or the distance to the preceding vehicle Vah is erroneously detected, a seriously dangerous situation occurs, for example, the subject vehicle comes close to and collides with the preceding vehicle Vah.
To avoid this situation, first, it is necessary to reliably determine whether or not there is a smear in the image. Accordingly, apparatuses that monitor brightnesses of all pixels in a taken image or brightnesses of pixels in a monitor region set in the image, and determine that a smear occurs when any of the pixels has a saturated or nearly saturated brightness have been developed (for example, see Japanese Unexamined Patent Application Publication Nos. 2000-207563, 2001-28745, 2001-43377, and 2002-22439).
Unfortunately, in a case in which only the brightnesses of pixels in the entire image or in the monitor region of the image are monitored, for example, when an image portion of a columnar object that glistens white because of reflection of the sunlight extends through the image from top to bottom, it may be erroneously detected that there is a smear. This may cause the ACC system to malfunction.
Even when only the monitor region in the image, not the entire image, is searched, much time is taken to constantly monitor the brightnesses of all pixels in the monitor region. Therefore, the processing time and the burden on the processing device are increased.